Switch



Jan. 2, 1940.- T L F NN T AL 2,185,433

SWITCH Filed July 2, 1938 INVENTORS I I and: Le me 500 ll l/fhrd 7T (IE (Nd? Patented Jan. 2, 1940 PATENT OFFICE z,185,433 swrron Thomas Legal- Fenn,

Newton, and Wilfred J.

' Turennc, Ashland, Mass.

Application July 2, 1938, Serial No. 217,296

11 Claims.

This invention relates to switches and more particularly to thermostatic switches for opening and closing electric circuits in accordance Y with thermal changes, especially thermal changes occurring externally of or otherwise affecting a device associated with, or containing, the switch.

In another aspect the invention relates to a formof switch which is completely assembled outside of the container orsother device with which the switch is to be operatively associated and thus constitutes a finished article of manufacture, which may be handled as'a unitary article when placing it in the device which forms its casing or otherwise assembling it in operative position.

about a form 'of switch for a thermally controlled instrument which may act as a safety device in an electric circuit and wherein the construction I is such that the switch will maintain a closed circuit while a series of operations, which it controls, are being performed correctly but will open in case of trouble, such as an improper operation of the. apparatus, and thus stop the operation by breaking the circuit. However, while the switch has special utility as a safety device, it is not limited to that specifl'c field but is capable of many other uses, for example, as a control switch for refrigerators or for air conditioning where a maintenance of uniform low tempera ture conditions is a requisite.

In the preferred embodiment of the invention the switch unit takes. the form of two opposed leaf springs bearing electrical contacts eflfectively connected together at their ends and bowed away from one another between their ends. A switch in this form can be constructed and sold as a unitary article of manufacture to those who desire to assemble it with electrically controlled apparatus.- A feature of the switch unit resides in a form -of construction which facilitates mounting the unit within a tube or other housing and providing for adjustment to vary the degree of temperature at which the unit becomes effective to perform its safety or other function.

To the accomplishment of this object and such others as may hereinafter appear, as will readily be understood by those skilled in the art, the invention comprises the features and combinations of parts hereinafter described and then particularly pointed out in the appended claims.

In the accompanying drawing,

Figure l is a perspective view of oneof the metallic springs, forming the switch unit as shaped for assembly with a like spring:

A general object of the invention is to bring Fig. 2 is an elevational view showing the inner face of the spring shown in Fig. 1;

Fig. 3 is a perspective view of a device for holding the two springs in assembled position, formed to also serve as an anti-twist flange when the switch unit is located in a housing.

Figs. 4 and 5 are views of the two elements secured, one at each end of the switch unit, for

mounting and centralizing the unit within a housing;

Fig. '6 is a sectional view of a screw for adjusting the tension 'of the switch when assembled in operative position;

Fig. is a perspective view of two of the springs of Fig. I placed face to face ready to receive the binding devices upon their tubular extensions;

Fig. 8 is a perspective view of the switch unit ready to be placed with the addition of two head pieces for producing a unitary-self contained article; and

Fig. 9 is a view, in cross-section, of a tubular housing with the switch unit installed and with an adjusting screw in place.

In the embodiment of the invention shown in the drawing for illustrative purposes, Ill (Fig. 8) indicates, in general, the improved switch unit which, in the form shown, includes a pair of leaf springs I I and I2, rigidly connnected together at their ends and bowing outwardly away from one another intermediate their ends. The springs I I and I2 are substantially identical and prior to assembly (Figs. 1 and 2) each consists of a single strip of flexible metal having a low coefficient of expansion, such as invar. The springs between their ends havea concave bowlike shape and'a thickness and width capable of giving the desired degree of stiffness. At their ends the springs are pressed, or otherwise formed into semi-cylindrical, concave-convex, straight extensions l3 (shown best in Fig. l). The two semi-cylindrical extensions at the opposite ends of each spring have their axes in alignment and their concavo sides at the concaved face of the bowed spring.

Substantially halfway between the ends of each spring II and I 2 is an electrical contact or switch point indicated by I l and I5. As shown, each contact is attached to a metallic clip I! or II, the latter being insulated from the springs "by mica or other suitable insulating material I8 and I9. The clips I6 .and Il may be tightly crimped around the springs with the mica insulation intervening, the contact being on the concave face ofeach bowed spring.

During the assembly of the switch unit th vised for binding the two switch springs together ly divided without departing from the scope of this invention, the tubular form being herein disclosed because it is the cheapest to manufacture. The rod-like mounting elements 20 and 2| (Figs. 4 and 5) are dimensioned to slip within these extensions.

A simple and inexpensive means has been deso that the assembly may be handled as a unitary article while securing the mounting rods in said extensions. The means for maintaining the two springs in the relation illustrated by Fig. 7 consists essentially of a'tubular member dimensioned to telescope over the tubular extension and bind its two sections, and thereby the springs, together. This member fits tightly and effects a rigid assembly. For convenience the binding member is formed as a part of an element functioning to prevent torsional twisting of the switch unit when in use and it will be so described.

In order to provide an arrangement for preventing twisting or rotational movement of the switch unit as a whole when assembled within a housing, head pieces 22 and 23 (Fig. 3) are assembled one on each end of the switch in position wherein they telescope over the extensions formed by the parts l3. Each head piece comprises a disc-like body 2 and a preferably, though not necessarily, integrally formed cen- -tral tubular boss 25, the bore 26 of each boss extending through its respective head and being of a diameter such that the head may be telescoped with a tight fit over either tubular extension of the switch unit. The pins and 2|, after insertion within the bosses are then spot welded at the bosses or these parts are otherwise rigidly secured together. The disclike body or flange 24 of one head piece (or both made alike for economy of manufacture) may be notched at diametrically opposite points 21 and 28 for a'purpose hereinafter described. The flanges 24 are also formed with diametrically opposite, relatively wide grooves 29 and 30 which provide clearance for circuit wires entering a switch casing passing to the switch points l4 and I5. The clips l6 and I1 have tongues 3i struck out of the material thereof to which the wires may be attached, as by solder or pressure.

The switch as thus assembled is shown in Fig. 8 and it will be apparent that this assembly either with or without the end pins is in the form of a unit which is self-contained and may be independently handled before embodiment in a thermostat or other device wherein it is useful. When not under tension the inherent bowed shape of the springs maintains the circuitthrough the contacts I and [5 open. If sufficient tension is applied to one or both ends of the unit in a direction tending to separate the ends, the springs will'be straightened, eventu-' ally causing the contacts to engage and close the circuit.

As an example of a suitable use to which the switch unit may be put, and in order that its mode of operation may be fully understood, it will now be described in connection with a the:-

mostat suitable for use in controlling the operation of an autoclave or the like, it being understood, however, that the description thereof in connection with this particular instrument is for illustrative purposes only.

Fig. 9 of the drawing indicates, in general, a thermostat suitable for use in opening an electrical circuit when the temperature to which the thermostat is subjected falls below a predetermined point. This thermostat comprises a cylindrical casing or tube 33 of brass or other material having a reasonably high coemcient of expansion. The tube 38 may be closed at its lower end by a head 34 bored axially at 35 to receive the lower mounting pin 20 of the enclosed switch unit [0. The upper end of the tubular housing may be closed by a head 38 threaded axially at 39 to receive an adjusting screw 40 (see Fig. 6), the latter being bored axially and threaded internally at ll to receive the threaded mounting pin 2! at the upper end of the switch unit. 'At diametrically opposite points the housing 33 may be pressed inwardly to form short longitudinal ribs 44 and 45 which are embraced by the diametrically opposite grooves 21 and 28 formed in the upper reenforcing head 22 of the unit. A single guiding rib may be employed if desired.

The heads 34 and 38 of the tube 33 may conveniently be secured in place by silver soldering, one of the heads being inserted after the switch unit III has been slipped within the housing, setting its lower mounting pin 20 in the bore 35 made for its reception. The pin 20 may then be made fast to the. housing by silver soldering. The external thread on the adjusting screw 40 and the internal threads ll therein are provided with difierential pitches such that rotational movement .of the screw 40 through-the head II will produce a longitudinal or axial movement of the upper mounting pin 2|, the lower pin 20 being fixed, to place the springs H and i2 of the unit under a desired tension.

It will be apparent that when the thermostat described above is subjected to the effect of heat the housing 33 will expand, and the switch unit III will elongate proportionally drawing the contacts I4 and it toward each other. Sufllcient tacts to engage and close the electrical circuit indicated by 46. By suitable adjustment of the screw 40 on the mounting pin 2| the effect of the expansion of the housing 33 may be varied to bring about a closing of the circuit at any desired temperature.

When using an autoclav for example for sterilizing surgical instruments, an assembly such as shown in Fig. 9, or any other assembly including the switch unit in an operative manner, may-be fastened in a selected location as on the inner panel of the door or in the steam exhaust. A valve in the steam line is mechanically connected to be shut oil when the circuit is broken. The switch unit is preliminarily adjusted to open at say 250 F., the temperature required to be maintained for the period required for sterilization. When the flow of steam raises the temperature within the autoclave to that degree the switch contacts close and stay closed unless the temperature, due to difllculty in the steam'line perhaps, drops below the critical degree. If that happens before expiration of the time limit for sterilization, the switch casing will contract, the switch will open and the steam will be shut off thus guarding against fallexpansionof the housing 33 will cause the conure of the autoclave to perform its function.

Thereafter .the cycle may be started again and, provided no mishap occurs, the instruments in sterilized condition, are removed from the autoelave when the cycle is ended automatically at the end of the predetermined period.

The method of connection of the springs to their mounting elements is such that variations in tension are directly applied to the springs unit during the adjustment thereof. The switch.

assembly as a whole is capable of use as a complete article of manufacture for introduction within a casing ofthe character described or for assembly in other devices wherein its features are of value. 4

While the particulars of construction herein set forth are well suited to one form of the invention, it is not to be understood that these particulars are essential since they may be variously modified within the skill of the artisan Without departing from the true scope of the actual invention as defined by the following claims.

What is claimed as new, is:

l. A switch unit for thermostats or the like comprising a pair of bowed metallic leaf springs arranged with their concave sides opposed, said springs each having a semi-cylindrical concavoconvex extension at each end the concave sides of which face inward in said assembly, whereby said concavo-convex extensions meet in pairs to form tubular extensions at each end of the assembled pair of'springs, means co-acting with each said extension to maintain the two springs in the relation described, and opposed, normally disengaged electrical contacts associated one with each of said springs on the concaved face thereof.

2. A switch unit for thermostats or the like comprising a pair of bowed metallic leaf springs arranged with their concave sides opposed, said springs each having a semi-cylindrical concavoconvex extension at each end the concave sides of which face inward in said assembly, whereby said concavo-convex extensions meet in pairs to form tubular extensions at each end of the assprings each havinga semi-cylindrical concavoconvex extension at each end the concave sides of which face inward in said assembly, whereby said concavo convex extensions meet in pairs to form tubular extensions at each end of the-assembled pair of springs, a tubular member telescoped over each saidextension for binding its two parts together and holding the two springs in the relation described, a. guide flange mounted on .at least one said extension adapted to prevent torsional twisting of the unit when in use, and opposed, normally disengaged electrical contacts associated one with each. of said springs on the concaved face thereof.

4. A switch unit for. thermostats or the like comprising a pair of bowed metallic leaf springs arranged with their concave sides opposed, said springs each having a semi-cylindrical concavoconvex extension at each end the concave sides of which face inward in said assembly, whereby said concavoconvex extensions meet in pairs to form tubular extensions at each end of the assembled pair of springs, a reinforcing head for holding the two parts ofsaid extension together consisting of a shorttube having a guiding flange at one end, said tube being of such internal diameter as to receive an extension with a tight fit, one of said heads being fitted on each said extension with, its guiding flange adjacent the spring ends, and opposed, normally disengaged electrical contacts associated one with each of said springs on the concaved face thereof.

5. A switch unit for thermostats or the like comprising a pair of bowed metallic leaf springs arranged with their concave sides opposed, said springs each having a semi-cylindrical concavoconvex extension at each end the concave sides of which face inward in said assembly, whereby said concavo-convex extensions meet in pairs to form tubular extensions at each end of the assembled pair of springs, a tubular member telescoped over each said extension for binding its two parts together and holding the two springs in the relation described, a mounting pin secured within the tubular extension at one end of the unit, and a threaded adjusting rod secured within the tubular extension at the other end of the unit, and opposed, normally disengaged electrical contacts associated one with each of said springs on the'concaved face thereof A 6. A metallic leaf spring for thermostatic switches bowed in one direction substantially throughout its working length and having a short portion at at least one ofthe ends thereof shaped to form a semi-cylindrical concavo-convex extension the axis thereof extending longitudinally of the spring and with its concavo side at the concaved face of the bowed spring.

'I. A metallic leaf spring for thermostatic switches bowed in one directionsubstantially throughout its working length and having both of its end portions shaped to form aligned extensions of concavo-convex contour.

8. A spring element for thermostatic switches comprising a strip of metal having a low coefl-a flcient of expansion bowed in one direction substantially throughout its working length, and

having end portions beyond the bowed part thereof in the form of semi-cylindrical concavo-convex extensions, said two extensions being axially aligned. T

9. A switch unit for thermostats, or the like comprising a pair of metallic leaf springs each bowed intermediate its ends, the bowed portion of each spring-having a longitudinal extension at each end thereof and said springs being assembled concaved face to concaved face with the ends of their bowed portions contacting in pairs, said end extensions opposing each other in pairs beyond each pair of contacting ends of said bowed portions, binding means co-acting with each such opposed pair of end'extensions for maintaining the bowed portions of the two springs in their-assembled relation, and opposed, normally disengaged electrical contacts associated one with each of said springs on the concaved fa'ce thereof.

10. A switch unit according to claim 9 in which said binding means comprises an apertured head piece at each end 01 the unit, each head piece being slipped over a pair of end'extensions and rigidly maintaining them intheir opposed relabowed portions, an apertured head piece at each end of the unit, each headpiece being slipped over a pair of end extensions and rigidly maintainiiig them in their opposed relation, each head piece having an outwardly facing socket for receiving a rod-like mounting element in further longitudinal extension beyond each end of the unit, and opposed, normally disengaged electrical contacts associated one with each of said springs on the concaved face thereof.

THOMAS LEGAR'E FENN. WILFRED J. TURENNE. 

